In a mobile telephony system with diversity reception in the base stations, each base station is equipped with two, or more than two antennas. In the reception mode, signals received from different antennas are added together in an appropriate manner, or optionally only the strongest signal at that time is chosen. Variations in the strengths of the received signals are caused by fading which in mobile telephony systems is caused by reflections of the transmitted radio signals, these reflections changing in time as the mobile station moves. For instance, when the base station is equipped with two antennas, the signal received on the one antenna may be of good quality whereas the signal received on the other antenna is of poor quality as a result of fading, whereas moments later the quality of signal reception on respective antennas may be the reverse.
When transmitting from the base station to the mobile station, it would be beneficial to transmit sometimes on the one antenna and sometimes on the other antenna, depending on which antenna produces the best received signal in the mobile station at that moment in time. Consequently, it is desirable to transmit from the mobile to the base station commands which are concerned with the selection of transmitter antenna in the base station. One problem in this regard, however, is that each transmission sequence (burst) in a time multiplex mobile telephony system of the GSM-type, for instance, already a predetermined content consisting of data bits and a synchronizing word.